1. Field of the Invention
This invention relates to a light-sensitive material for preparing a lithographic printing plate and a process using the same and, more particularly, to a light-sensitive material for preparing a lithographic printing plate containing both a light-sensitive silver halide layer and a layer of a positive-working light-sensitive resin composition and having high sensitivity and camera speed, and a process for processing the same.
2. Discussion of the Prior Art
The term "camera speed" indicates that the light-sensitive material in question is photographically sensitive enough to permit imagewise exposure by focusing an original onto the light-sensitive layer of the printing plate forming material through an image-focusing lens system. On the other hand, the term "contact speed" means that a light-sensitive material has sensitivity such that it can be exposed through a negative or positive transparency placed in contact with it.
Most light-sensitive lithographic printing plate materials presently in commercial use are of contact speed sensitivity. Thus, an image-bearing transparency of the original must be prepared before a printing plate can be made from a contact speed material and the number of steps necessary to prepare the lithographic printing plates is considerably more than in the case in which no transparency is necessary.
The sensitizers typically used in light-sensitive lithographic printing plate materials are diazo compounds, o-quinonediazide compounds, or light-sensitive polymers like polyvinyl cinnamates. However, the photographic speed of these materials is too slow for the materials sensitized therewith to be of camera speed. Therefore, most light-sensitive lithographic printing plate making materials are of contact speed as previously described. The most common sensitizer used in photographic materials of camera speed is silver halide, and light-sensitive lithographic printing plate materials having solely a silver halide emulsion layer as the image-forming layer have been produced. However, such plate materials are comparatively difficult to process and the printing life thereof is not long, i.e., the number of prints which can be printed with them is not very great.
Other light-sensitive lithographic printing plate materials of camera speed are known. These materials are composite materials comprising a support having provided thereon a light-sensitive layer of contact speed and further a silver halide emulsion layer of camera speed. Examples are described in U.S. Pat. No. 3,567,445, Japanese Patent Application (OPI) No. 62501/77 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") (corresponding to U.S. Application Ser. No. 899,680, filed Apr. 24, 1978), U.S. Defensive Publication No. T 870,022, U.S. Pat. No. 3,578,451, etc.
In these composite light-sensitive lithographic printing plate materials, the light-sensitive layer of contact speed is oleophilic, and hence it is necessary to provide an interlayer or undercoating having good adhesion to both the hydrophilic silver halide emulsion layer and the oleophilic light-sensitive layer between them as described in British Pat. No. 1,187,980 and U.S. Pat. No. 3,567,445. Japanese Patent Publication No. 13128/65 describes a material without an interlayer for improving adhesion, but it is well known in this field that such materials are not practical since the silver halide emulsion layer peels from the oleophilic surface upon development processing the emulsion layer.
Japanese Patent Application (OPI) No. 62501/77 discloses that light-sensitive compositions prepared by dispersing silver halide grains coated with a hydrophilic polymer in an oleophilic polymer dissolved in an organic solvent provide light-sensitive lithographic printing plate materials having good adhesion when the silver halide emulsion layer is coated directly on a layer of an oleophilic light-sensitive composition of contact speed without an interlayer. However, in this process it is difficult to disperse the silver halide light-sensitive emulsion coated with the hydrophilic polymer in the organic solvent containing the oleophilic polymer and a deflocculant (e.g., salicyclic acid, acetic acid, etc.) for the hydrophilic polymer is necessary for dispersion. As a result, the workability of the process is extremely bad, for example, the hydrophilic polymer is often flocculated in a gel form upon preparation.
According to U.S. Pat. No. 3,567,445 composite light-sensitive lithographic printing plate materials are processed as follows. First, the silver halide emulsion layer is imagewise exposed, developed, fixed, and washed with water to form a silver image. Then, the light-sensitive layer of contact speed is exposed to ultraviolet rays through the silver image. After removing the silver halide emulsion layer, the light-sensitive layer of contact speed is developed. Thus, development processing of the silver halide light-sensitive layer is complicated and two additional steps of removing the light-sensitive layer of camera speed and developing the light-sensitive layer of contact speed are necessary.
Japanese Patent Application (OPI) No. 62501/77 describes removing the silver halide light-sensitive layer and developing the light-sensitive layer of contact speed in one step. That step is conducted by selecting an organic solvent which can be used to both develop the light-sensitive layer (dissolve the exposed portions in the case of a positive-working material or the unexposed portions in the case of a negative-working material) and remove the silver halide layer (dissolve the silver image portions). However, from a practical standpoint, it has been found that the use of such an organic solvent swells the image portions of the light-sensitive layer of contact speed and the strength of the image portions is reduced, resulting in deterioration of durability and image quality.
Example 8 of U.S. Pat. No. 3,511,661 describes a light-sensitive lithographic printing plate forming material comprising an aluminum support having an anodized aluminum oxide layer provided with a negative-working light-sensitive resin layer containing 4,4'-diazidostilbene and in contact therewith an unhardened gelatino silver chloride emulsion layer containing a tanning developing agent (3,4-dihydroxydiphenyl or 4-phenylcatechol). Also disclosed is a process of preparing a lithographic printing plate using this material by imagewise exposing it, dipping it into a sodium hydroxide aqueous solution to activate and conduct tanning development, spraying warm water (43.degree. C.) on the plate to leave a hardened silver image relief on the light-sensitive resin layer, and drying. The thus developed plate is uniformly exposed to light, developed with benzyl alcohol to remove the hardened silver image relief and the underlying unexposed light-sensitive resin layer and leave only the exposure-hardened light-sensitive resin layer on the hydrophilic aluminum support. The plate is then subjected to desensitization processing, and used to print several thousand copies using the resultant lithographic printing plate. This material and processing are clearly different from that of the present invention in the following points: (i) the light-sensitive resin is negative-working; (ii) the material contains no tannable interlayer; (iii) no hardened silver image relief is formed on the developed light-sensitive resin layer and used in printing; and (iv) the light-sensitive resin layer developer is an alkali-free organic solvent. The number of printed copies is as small as several thousand, which is greatly smaller than the number of printed copies (about 100,000 to 150,000) attained in the present invention.
U.S. Defensive Publication No. T 870,022 describes a composite light-sensitive lithographic material comprising a support having a hydrophilic surface provided thereon, in order, with (a) a layer containing light-sensitive organic soluble polymer, (b) an interlayer such as a gelatin-cellulose nitrate undercoating or a gelatin-sodium silicate undercoating, and (c) a light-sensitive emulsion layer such as a silver halide emulsion layer. This material is clearly different from the light-sensitive material of the present invention in the following regards. First, the interlayer tends to delaminate from light-sensitive layer (a) in the presence of organic processing chemicals. Second, the tannable interlayer in the invention material may contain both a tanning developing agent and silver halide which makes it clearly different from the above-described interlayer (b).
U.S. Pat. No. 3,578,451 describes a composite light-sensitive lithographic plate forming material wherein an intermediate water-barrier coating and a silver halide emulsion layer are provided on a negative-working light-sensitive lithographic plate material. This is clearly different from the material and process of the present invention in that the light-sensitive layer is negative-working, n-propanol is used for developing the light-sensitive resin layer, and the entire silver halide emulsion layer is removed by the development with n-propanol. In addition, the number of printed copies is as small as about 10,000.
Extensive investigations directed to overcoming the above-described defects of conventional lithographic printing plate forming materials of camera speed have resulted in the discovery that strong adhesion is attained between a silver image and a light-sensitive layer of contact speed by imagewise exposing a composite light-sensitive lithographic printing plate forming material comprising a tannable interlayer containing the same polymer as the binder polymer of the light-sensitive silver halide emulsion layer, and a light-sensitive silver halide emulsion layer containing a tanning developing agent, and conducting tanning development through alkaliactivation processing which is a preferred embodiment.